Alkanoic Acids (carboxylic Acids)

Alkanoic acids are organic compounds that contain a carboxylic acid functional group (–COOH). Their general molecular formula is C_nH_2n+1COOH. They are commonly found in fats and oils.

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Examples of Alkanoic Acids

1. Methanoic acid (Formic acid): HCOOH – found in insect bites
2. Ethanoic acid: CH₃COOH
3. Propanoic acid: CH₃CH₂COOH

Preparation

Alkanoic acids can be prepared in the laboratory by oxidizing primary alkanols using excess acidified potassium tetraoxomanganate (VII).

Physical Properties

• Colourless liquid with a sharp, pungent smell
• Sour taste
• Soluble in water
• Freezes into ice-like crystals below 17°C; thus known as glacial ethanoic acid (anhydrous ethanoic acid)
• Boiling point of 118°C
• Turns blue litmus paper red

Chemical Properties

1. Reacts with carbonates or hydrogen carbonates to release carbon dioxide:
   2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
2. Reacts with reactive metals like Ca or Mg to liberate hydrogen gas:
   2CH₃COOH + Ca → (CH₃COO)₂Ca + H₂
3. Neutralizes bases (alkalis) to form salt and water:
   CH₃COOH + NaOH → CH₃COONa + H₂O
4. Reacts with alkanols to form esters (esterification):
   CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃ + H₂O
5. Reduction: Reduced to ethanol using lithium tetrahydridoaluminate(III) (LiAlH₄):
   CH₃COOH + 4[H] → CH₃CH₂OH + H₂O
6. Successive reaction with chlorine to form chlorinated ethanoic acids:
   CH₃COOH + Cl₂ → CH₂ClCOOH + HCl
   CH₂ClCOOH + Cl₂ → CHCl₂COOH + HCl
   CHCl₂COOH + Cl₂ → CCl₃COOH + HCl

Classification of Alkanoic Acids

1. Monocarboxylic Acids: Contain one carboxylic group per molecule (e.g., Methanoic acid - HCOOH)
2. Dicarboxylic Acids: Contain two carboxylic groups per molecule (e.g., Ethan-1,2-dioic acid or oxalic acid)
3. Tricarboxylic acids: these have 3 carboxylic acid per molecule (e.g. 2-hydroxy propan 1,2, 3, tricaboxylic acid)

Uses of Ethanoic Acid

1. Used in making compounds such as cellulose ethanoate and dyes
2. Serves as an organic solvent
3. Used in the food industry for preservation and flavoring
4. Used in coagulating rubber latex